🔍 Key Concepts

• MODU (Mobile Offshore Drilling Unit) draft and structure relative to the sea surface • Difference between air gap, draft/penetration, and freeboard • Reference level: still water level corrected for tides and storm surge

💭 Think About

• Ask yourself: Is the measurement going upward into the air from the water, or downward into the water from the surface? • Which term is normally used for the distance from waterline to the top of the hull or deck, and which for the distance from waterline to the lowest underwater point? • On a MODU, what term describes how far the hull is below the sea surface, affecting how close the seabed can be?

✅ Before You Answer

• Identify whether the question is talking about the part of the structure above water or below water. • Recall that freeboard is commonly measured from the waterline upwards to a deck or reference point on the hull, not downwards. • Remember that air gap relates to the distance between the underside of the deck/hull and the sea surface, often for wave clearance, not penetration below the water.